1. Field of the Invention
The present invention relates to utility knives, and methods of making such knives. More particularly, the present invention relates to utility knives which are particularly adapted for use in cutting open corrugated cardboard shipping boxes, and include also a cutting guide serving to guard the exposed end of the cutting blade in such use. Still more particularly, the present invention relates to such utility knives which include a somewhat bulbular or ergonomically-shaped handle or body, a cutting blade movable in the body to extend a cutting portion of the blade outwardly of the body at one end of the latter, externally accessible means for moving the cutting blade between the extended cutting position and a retracted position of withdrawal into the handle, and provision for storage of several spare blades within the handle.
2. Related Technology
The field of utility knives includes many examples of previous attempts extending over many years all directed to providing a utility knife which satisfies one or more of the many concerns for such knives. Among the concerns addressed are making a utility knife which is inexpensive, safe in a variety of uses, rugged, reduces or prevents damage to the contents of cardboard boxes opened with the knife, is durable, easy to use, is easily grasped and provides good purchase on the knife for security and certainty in its use even while the user's hands may be moist and slippery, reduces the fatigue inherent in some of the strenuous uses of hard cutting for which such knives are used, provides conveniences in the use and maintenance of the knife, is attractive, and provides for the storage of spare knife blades within the utility knife itself.
For example, U.S. Pat. No. 3,192,624, issued in 1965 to D. Gringer, is believed to teach a utility knife in which a handle provides a forward longitudinal cavity in which is slidably received a blade carrier member, and a rear cavity in which are received a number of spare blades. The blade carrier member carries a double-ended cutting blade, and is movable longitudinally of the forward cavity between a retracted safety position with the blade entirely within the handle, and an extended cutting position in which a triangular end part of the blade extends forwardly out of the handle. The handle is vertically split and includes two portions which are almost mirror images of one another. A screw secures the two handle portions together and allows their separation with the use of a screwdriver for substituting one of the spare blades for a used cutting blade. A similar utility knife is presented in U.S. Pat. No. 3,879,847, issued in 1975 to D. Roll in which blades may be changed without disassembly of the handle by forward extension therefrom of a forward part of a channel-like blade carrier member. As Roll points out, his utility knife no longer requires the inconvenience of carrying a screwdriver with which to open the handle of prior utility knives. However, his knife also appears not to offer the convenience of spare blade storage in the knife handle.
An alternative type of utility knife is represented by the 1931 German Patent No. 531,248, and descendants of the disclosed design. This design of utility knife includes a flattened tubular handle, with a blade carrier slidable in the handle between a retracted position sheathing the blade entirely in the handle, and an extended cutting position in which part of the blade is exposed forwardly of the handle. A spring-arm part of the blade carrier includes a lug receivable in detent notches of the handle to retain the carrier in selected positions, including the retracted position and various positions of blade extension. A button member is secured to the spring arm for disengaging the lug from the detent notches and moving the blade carrier to a selected position. Some members of this design family include differing handle designs, differing means of securing the blade carrier in position, and use differing types of blades. For example, the common single-edge razor blade is a favored blade for many of these utility knives although it has many deficiencies in such use. That is, the razor blade is brittle, thin, and not very rugged. Consequently, a razor blade may break off if, for example, a twisting or bending moment is imposed on the blade in use. Certain other of these knives use a trapezoidal-shaped double ended all-purpose (AP) blade, which is considerably more rugged than a razor blade.
U.S. Pat. Nos. 2,840,903; 3,195,231; 3,525,152; 3,621,570; and 4,570,342, may be considered as representative design descendants of the 1931 German patent discussed above. Generally, this type of knife is made with a handle of folded sheet metal, having a rather small edge radius opposite to the blade edge and against which cutting pressure may be exerted by the user. All of these knives are relatively thin, and provide only a small handle edge surface area against which manual cutting pressure may be exerted. This small handle edge radius and small edge surface area can combine to make many of these knives uncomfortable to use, especially in hard cutting use. Even when the user is wearing gloves, some of these knives are so thin that an uncomfortable pressure groove is soon formed in the user's hand after a period of hard cutting. Users then find themselves shifting the knife in their hand to avoid the sensitive pressure groove, and in the process attempting to use the knife in a less than optimum grasp. Understandably, this type of use contributes to fatigue and injuries. While some of these knives provide a handle with somewhat increased manual surface area, all are deficient to some degree with respect to the grasp or purchase on the knife afforded to a user. Especially in hard use, the thin, fragile, or difficult to control knives of the above category are not well accepted by users.
A further branch of design in the utility knife area is represented by those utility knives adapted more especially for their use in opening cardboard cartons or boxes. In this use, the carton is generally held in front of the user with one hand and arm, and is cut by drawing the knife with the other hand toward the user across the side wall of the carton. Because such use frequently involves the need for speedy work, and the cardboard does present considerable resistance to cutting, flesh wounds are common when the knife blade springs free at the end of a cut and catches the user's arm. In this use particular attention must be given to protecting both a user of the knife, and the contents of a cardboard carton to be opened with the knife, from being inadvertently cut. For this use, U.S. Pat. No. 3,178,812, issued in 1962 to A. J. Lurie, depicts a utility knife having a pair of spaced apart plate-like blade guards, one for within and the other for outside of a carton. The inner guard is to protect the carton contents during cutting of the carton sidewall, and is carried at the end of a hook-like extension of the handle. This type of utility knife would seem to present inconveniences in use because of the necessity to provide for entry into the carton of the inner plate-like guard. A similar hook-like guard is seen in U.S. Pat. No. 4,167,810, issued in 1979 to R. Gilbert. The Gilbert teaching includes a formed wire hook-like inner guard for protecting the contents of a carton from the blade while the carton is opened. A hard point is provided for punching a hole in the carton for subsequent insertion of the formed wire hook.
An alternative form of blade guard, this one for protecting the knife user, is seen in U.S. Pat. No. 4,675,996, issued in 1987 to T. DuBuque. The Dubuque knife includes a pair of spring-loaded pivotal guard plates secured to the handle of the knife in such a way that they are asserted to prevent accidental exposure of the blade edge. The guards are stated to pivot and expose the blade edge when the knife is drawn along the side of a carton. The guards are said to roll on the cardboard surface. Why these pivotal guard plates would not also pivot away to expose the blade if the knife were inadvertently drawn across the user's arm, for example, is not clear from the patent.
An alternative form of blade guard for protecting both user and carton contents is depicted in U.S. Pat. No. 4,744,146, issued in 1988 to G. G. Schmidt, and owned by the assignee of the present application. In the Schmidt knife a planar plate-like guard member lies adjacent to, but spaced from, the blade in its extended carton-opening position. The plate-like guard member provides a guide surface by which the knife may be guided along the top corner of a carton to be opened while the carton side wall is cut to remove the carton top. Because the edge of the blade is recessed behind the edges of the guard plate, a user of the knife is not likely to be cut with the knife. Also, because the blade penetrates the side wall of the carton a controlled amount immediately adjacent to the top inside wall of the carton, the contents are not likely to be injured by the blade. The Schmidt knife also offers a considerably improved ease of use because its handle is formed of a sturdy aluminum extrusion offering a considerably larger surface area against which cutting pressure can be applied by a user of the knife, as well as more comfortable rounded outer edge surfaces of larger radius than some other knives. This knife also includes features avoiding accidental dropping of the worn blade when replacing the blade is necessary, and provides for storage of several spare blades within the knife.
A similar guard member is seen in U.S. Pat. No. 5,054,198, issued in 1991 to R. Gmoch, differing so far as the guard feature is concerned only in the angular relation of the guard to the length of the cutting blade.